"The quick action by a passerby who reported it, and the Fire Brigade getting there quickly is the only reason we have a building," Ms Eaton said.

The Tukapa St Westown building, which houses doctors, nurses, physiotherapists, radiology services and a pharmacy, is the city's biggest medical centre. Ms Eaton first found out about the fire when the cleaner, working alone in the building that morning, rang Ms Eaton in a panic about 6.15am.

The cleaner only found out there was a fire when she went outside to put rubbish in the bins on the side of the building.

The passerby, waiting for the brigade to arrive, warned her of the fire around the front of the building.

"We'd like to track them down to say thank you," Ms Eaton said. Ms Eaton said there was little sign of a fire when she arrived about 15 minutes later.

"It didn't look like much at that time but it escalated very quickly.

"The fire brigade was amazing."

The news that a man was arrested and now in custody was a great relief to the staff, she said.

The man is charged with intentionally damaging the centre by fire knowing that danger to life was likely to ensue.

Sandy Teika Fredrick Hauwaho, 27, agreed to a remand in custody during his short appearance in the New Plymouth District Court.

Duty lawyer Josie Mooney said Hauwaho would be filing a bail application. Police opposed him being released on bail.

Hauwaho was remanded to appear on Thursday.

Officer in charge of the arson investigation, Detective Sergeant Gerard Bouterey, of the New Plymouth CIB said Hauwaho had only been living in the city a short time.

Ms Eaton said patients had been extremely supportive in the aftermath. "One lovely patient even brought us morning tea."

It was fortunate several doctors were away on holiday. Seven consulting rooms and the nurses' station were still out of action.

Radiology re-opened yesterday and the pharmacy, which was without power until Monday, was now back in operation.